He did not utter the words, but President Barack Obama’s second inaugural address was suffused with the spirit of a favorite phrase: Martin Luther King Jr.’s call to heed “the fierce urgency of now.”

This was a president unbound from much of what defined him upon taking office four years ago, a man clearly cognizant of time already running down on his opportunity to make his imprint on the country and on history.

Gone were the vision of a new kind of high-minded politics, the constraint of a future re-election campaign and the weight of unrealistic expectations. In their place was an unapologetic argument that modern liberalism was perfectly consistent with the spirit of the founders and a notice that, with no immediate crisis facing the nation, Obama intended to use the full powers of his office for progressive values.

“We must act, knowing that our work will be imperfect,” he said.

After spending much of his first term “evolving” on the question of gay marriage and doing too little in the eyes of many African-Americans to address poverty and civil rights, he invoked “Seneca Falls and Selma and Stonewall” and cited responsibility for the poor, sick and displaced.

He acknowledged the budget deficit but emphasized protecting Medicare, Medicaid and Social Security. He mentioned jobs but highlighted global warming. He lauded the bravery and strength of the U.S. armed forces, but started his foreign policy remarks by asserting that “enduring security and lasting peace do not require perpetual war.”

Obama came to office four years ago all but consumed by what he inherited: two wars and an economy in free fall. He then confronted an exhausting series of crises and political problems at home and abroad: budget showdowns, a huge oil spill, Middle East turmoil, the rise of the Tea Party movement.

Through it all, he chose to wage additional battles of choice, most notably his successful push to overhaul the health insurance system. But not until this point, with the economy gradually mending, one war over and another winding down, with Osama bin Laden dead and the Democratic Party drawing strength from the nation’s changing demographics, has he had the opportunity to master his own presidency.

The policy details of what that effort entails will emerge over the next month through his State of the Union address and his budget, and many or most of them will encounter strong opposition from Republicans on Capitol Hill. Monday’s address to the nation and its political class was intended to set out the value system that informs the policy.

But since Election Day, he has seemed to be choosing between them more than in the past. His decision after the Newtown massacre to embark on a full-scale effort to crack down on gun violence showed him to be less shackled to political wisdom about what is possible or electorally wise; his willingness to stare down Republicans over raising the debt limit — and winning — showed that he is less likely nowadays to start a negotiation by moving to the center and trying to find common ground.

To some Republicans, it is what they warned of all along: a president who ran as a centrist proving to be an unreconstructed liberal. It was no doubt hard for some of them to accept a scolding for treating “name calling as reasoned debate” — a phrase in his Monday address — from a man who won re-election by excoriating Mitt Romney as a job-killing plutocrat.

“I think all Americans would hope that President Obama, now that he’s not facing re-election, would actually sit down and honestly work with Republicans who are very sincere in our desire to fix these problems,” said Sen. Ron Johnson, R-Wis.

But, Johnson added, that was not the sentiment he detected from Obama on Monday. “You’ve got to sit down in good faith,” he said. “But I just don’t see that with this president.”

Obama’s address nodded to ideological inclusiveness but without repeating his view from four years ago that it was time to end the “recriminations and worn-out dogmas” that characterized Washington battles. It recognized the power of individual liberty but argued that only through collective action could the nation remain prosperous and secure.

But most of all, it sought to elevate to a more prominent place in the political debate the question of how best the nation should address the “little girl born into the bleakest poverty,” the parents of a child with a disability, the gay men and women seeking to marry, voters facing hurdles because of their race and immigrants seeking a toehold in a land of opportunity.

“We do not believe that in this country, freedom is reserved for the lucky, or happiness for the few,” Obama said.

In many ways it was an inaugural address, given on a day that commemorates King, that reflected not just the civil rights leader’s “fierce urgency of now” but the lines that immediately followed it in his “I have a dream” speech on the National Mall 50 years ago.

“This is no time to engage in the luxury of cooling off or to take the tranquilizing drug of gradualism,” King said. “Now is the time to make real the promises of democracy.”